1. Field of the Invention
This invention relates generally to a medical device for marking a target site within a tissue mass and more specifically to a medical device having a marker for marking a biopsy site in breast tissue that is deployed after the breast tissue has been decompressed.
2. Description of the Related Art
A biopsy is a well-known medical procedure that involves taking a sample of tissue from a person and examining it for diagnostic purposes. This is often done when an abnormality is found in a tissue mass, for example when a lump is found in breast tissue or when an imaging system, such as mammography or ultrasonography detects a suspicious area. Examining a sample of tissue from an abnormal site or lesion is currently the only way to accurately diagnose cancer.
A vacuum-assisted biopsy (VAB) uses an imaging system, such as ultrasonography or mammography, to locate a lesion in the breast tissue and to guide a biopsy probe to the site. An example of a known VAB device 200 is shown in FIG. 1. Such a VAB device is described in U.S. Pat. No. 6,712,774 and is incorporated by reference in its entirety. The details of the VAB device are not germane to the invention and thus will only be briefly described. The probe 70 has a pointed tip 76 to facilitate its insertion through the tissue mass, an opening 78 in the side wall of the probe near the pointed tip, and a vacuum chamber 72. Once the probe 70 is in position at the lesion site, a vacuum pump creates a vacuum in chamber 72 and draws the tissue through the opening 78 and into a sampling chamber where a cutting device is advanced through the probe 70 to cut and remove a tissue sample. Other instruments can be inserted through the probe 70 in addition to the cutting device.
The position of the patient during VAB depends on the imaging system used to locate the lesion and position the probe. If ultrasonography is used, the patient will be in a supine position. If mammography is used, the patient typically lies prone on a specialized table such that the breast protrudes through a hole in the table. The breast is compressed between two plates while an image of the lesion is produced on a monitor by a mammography unit. Once the lesion is imaged, the VAB probe, which is mounted to the table or the mammography unit, is inserted into the breast tissue and the tissue sample is gathered as described above.
In some cases, it is desirable to mark the location of the lesion site in case a future biopsy or surgery is necessary. This is done with a marker that is made of any suitable material that can be imaged by an imaging system, such as ultrasonography, magnetic resonance, or mammography, or that is palpable through the skin and tissue of the patient. The marker must be accurately placed at the lesion site in the breast tissue and must remain at the site so that the lesion can be located and identified at a later time, if necessary. However, there sometimes is a need for a marker to be repositioned after its initial placement, such as if the marker was not placed at the desired location or if the marker shifts upon decompression of the tissue. Thus, the marker must be able to remain anchored in the breast tissue, yet permit its repositioning.
One type of marker is a biocompatible clip that can be placed at the lesion site to facilitate locating the lesion during later procedures. The clip has the advantage of being implanted entirely within the tissue mass, so that there is no possibility of accidental repositioning by pulling or tugging the clip. The clip is placed after the tissue sample has been gathered from the lesion site and while the breast is still compressed. The clip is inserted into the tissue mass through the VAB probe and thus does not require the tissue mass to be repierced. Since the clip is deployed when the breast tissue is compressed, upon decompression the clip may be found to be implanted away from the lesion site, leading to inaccurate marking of the lesion site. An illustrative example of the post-decompression shifting problem is a rubber ball that is normally 5 cm in diameter, but compressed to 2 cm. If a clip is to be placed 1 cm from the edge of the ball, the clip would be placed at the center of the ball. However, if upon decompression of the ball the clip stays at the center of the ball or shifts away from the target site, the clip is misplaced by up to several centimeters. Coopers ligaments in the breast exacerbate the problem of inaccurate marking by acting to pull the clip away from the site of implantation when the breast is uncompressed.